The invention relates to a method for producing Schottky diodes having a protective ring in an edge region of a Schottky contact. The invention furthermore relates to a Schottky diode.
During the production of very small-area Schottky diodes, that is to say of Schottky diodes having a diameter of the order of magnitude of 5 to 10 xcexcm, eliminating the edge effects poses considerable difficulties. It is known to reduce the edge effects by use of a doped protective ring being introduced into the semiconductor substrate and/or into the topmost epitaxial layer using implantation technology. In the case of very small-area Schottky diodes, however, a doped protective ring produced by photomasks constitutes such a considerable additional capacitance that Schottky diodes produced in such a way cannot be used in relatively high frequency ranges. applications in the 77 GHz frequency range demand that the Schottky diode have a total capacitance of approximately 40 fF, which permits a parasitic capacitance of at most 10 fF.
It is accordingly an object of the invention to provide a method for producing Schottky diodes which overcomes the above-mentioned disadvantages of the prior art method of this general type, which have typical diameters of 5 to 10 xcexcm and can be used in high-frequency ranges typically of 77 GHz and above.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing a Schottky diode. The method includes the step of providing a semiconductor layer having a surface. A mask layer is produced on the semiconductor layer. The mask layer is formed so as to leave a region free of the mask layer on the surface of the semiconductor layer, the region provided for forming a Schottky contact. The mask layer and the semiconductor layer are covered by a barrier metal layer having edges for forming the Schottky contact. A ring shaped area remains free on the surface of the semiconductor layer between the mask layer and the edges of the barrier metal layer. The ring shaped area is covered by a high barrier metal and the high barrier metal forms a protective ring.
The invention provides for the protective ring to be produced after the production of the Schottky contact by depositing an electrically conductive protective ring material onto the surface of the semiconductor layer, which surface is provided with a patterned masking layer.
Following the principle of the invention, the protective ring material constitutes a metal, in particular a high barrier metal, which has, in particular, platinum.
The protective ring material is expediently applied by vapor deposition or by being sputtered on.
A further preferred embodiment of the invention may provide for the patterned masking layer to be etched back by undercutting prior to the deposition of the Schottky contact material using a patterned covering layer.
In accordance with an added feature of the invention, there is the step of applying the high barrier metal to a thickness of approximately 0.1 xcexcm.
In accordance with an additional feature of the invention, there is the step of forming the mask layer as a two-part layer formed of a silicon oxide layer and, on top of that, a silicon nitride layer is applied and the mask layer is patterned. The silicon nitride layer is undercut for forming overhanging rims.
In accordance with another feature of the invention, there is the step of applying the silicon oxide layer to a thickness of approximately 0.2 xcexcm and applying the silicon nitride layer to a thickness of approximately 0.1 xcexcm.
In accordance with a further feature of the invention, there is the step of forming the barrier metal layer by depositing titanium to a thickness of at most 0.1 xcexcm.
In accordance with a concomitant feature of the invention, there is the step of forming the semiconductor layer from silicon and siliconizing the high barrier metal after its applied.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for producing Schottky diodes, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.